In recent years, use of various types of video delivery services via broadband lines has been increasing. Along with the increasing, a multicast communication method is attracting attention. Japanese Patent Application Laid-Open No. 1999-331237 (paragraph [0003]) discloses a communication method, in which data transmitted from a server for video delivery is simultaneously distributed to plural clients on the viewer's side. A terminal on the viewer's side, which enjoys the service, needs to subscribe to a group called a multicast group. Protocol, which processes the subscription or unsubscription to the multicast group, is updated frequently because of increasing of use and enhancing of security level for the image delivery service, with the increasing demand of the services.
Regarding to the protocol to manage a subscriber to the multicast group, IGMP (Internet Group Management Protocol) has been proposed corresponding to IPv4 (Internet Protocol Version 4). Corresponding to IPv6 (Internet Protocol Version 6), MLD (Multicast Listener Discovery) has been proposed.
At present, the latest version of IGMP is the version 3. The latest version of MLD is the version 2. In each of the IGMP and the MLD of version released previous to the latest version, the multicast group is determined based on only a destination address. However, the latest version has been specified so that the multicast group is determined based on a combination of the destination address and a source address.
FIG. 15 is a block diagram illustrating a multicast data distribution system of the related art, where the version of the protocol is previous to the latest version. The version of the IGMP is the version 1 or 2, and the version of the MLD is the version 1.
Referring to FIG. 15, a multicast data distribution system 700 of the related art includes a router 701, a multicast distribution server 703 connected to the router 701 via a broadband line 702, and first to fourth terminals 7041-7044 on the viewer's side connected to the router 701. The first to fourth terminals 7041-7044 subscribe to the multicast group using a MLDv1 (Multicast Listener Discovery version 1) packet or a IGMPv1 (Internet Group Management Protocol version 1) packet. The multicast distribution server 703 transfers multicast data 706 to the first to fourth terminals 7041-7044, which subscribe to the multicast group.
The router 701 is provided with a network processor 713. A ROM (Read Only Memory) 711 for storing a control program to perform communication control and a RAM (Random Access Memory) 712 to temporarily store various types of data used for the communication control are connected to the network processor 713. The network processor 713 is connected to a layer 2 switch (L2SW) 714 via MII (Media Independent Interface) 716 and a management interface 720. The network processor 713 is connected to a physical layer integrated circuit (PHY) 715 via MII 717 and a management interface 721. The layer 2 switch 714 is connected to the first to fourth terminals 7041-7044 via a first to fourth LAN (Local Area Network) ports 7181-7184. In the following, an interface of the layer 2 switch 714 used for terminal connection is described as a port.
Assume that in the multicast data distribution system 700, the first terminal 7041 requests a delivery of video data from the multicast distribution server 703. The first terminal 7041 transmits an MLDv1 report message or an IGMPv1 report message (hereinafter, simply referred to as a report message) 722 to the router 701. The report message includes a report relating to subscription or unsubscription to the multicast group. The network processor 713 receives the report message 722 via the layer 2 switch 714 and the MII 716. The network processor extracts the destination address (DA) and a destination port, to which the data is forwarded, from the report message 722. The network processor 713 stores an analysis result into a MAC (Media Access Control) table 731 provided in the layer 2 switch 714.
In the specification, in order to make description clear, a destination MAC address is described as a destination address, and a transmission source MAC address is described as a source address.